The absorption, distribution, metabolism and excretion of p-phenylenediamine (PDA) has been studied in male and female rats and mice. PDA is readily absorbed, distributed to all tissues, metabolized and excreted mainly in urine in the form of several metabolites in both rats and mice. The rate of clearance from the tissues is fairly rapid and the whole body half-life is less than 12 hours. Only muscle retained significant quantities (4-7%) of PDA-derived radioactivity 24 hours after an iv dose. Quantitative and qualitative differences were observed between rat and mouse urine metabolites.